This may be what your colleague from work was referring to? Presumably without know it ;-)
Building web apps in C# on the other hand is a different story. It's a valid question.
C# has a mature framework for building Webforms or MVC apps (as well as Web API, REST and other services, etc) and uses Microsoft's Visual Studio. You can crank out some advanced functionality relatively quick. This is what I do for a living.
But achieving relatively quick in C# requires knowledge - lots of it. Depending on what you need, it's either a steep learning curve or requires well-paid talent.
I'm going to take a wild guess and say that the reason this conversation at work started, was because someone wondered how they could scale-up one or more of your web applications?
If this is the case, then not anticipating scaling up from the beginning of the project is not an easy thing to fix afterwards - regardless of what the app was built in.
Disclaimer: I'm not familiar with Xojo Web apps or the Xojo "Cloud" (I'm here for the Desktop and Mobile goodies).
But maybe the Xojo Cloud is designed to scale automatically by just adding more servers? It's worth asking, if you haven't already. If it can, than the cost of those extra servers will be much less than extra staff.
Anyway, if you want to learn more about the principles of scaling a web app, let me know. I hope some of this helps.
My apologies for the long read and any wrong assumptions about your knowledge level.
All the best!